My suggestion is to replace with an aluminum pan. They are a little more expensive but they seal and also keep your transmission cooler.

Chrome anything rarely seals. The only way that I have gotten any chrome part to seal is to take my die grinder and a sanding disc to the sealing surface. This will create a sealing surface for the gasket to adhere to. Chrome transmission pans are the worst. Also, if the bolt holes are bowed up a little, which happens a lot due to over torquing, A wood block and a ball peen hammer will get the holes back to normal.